This invention relates to generally to cryotherapy. More specifically, this application relates to image-guided control of cryoprobes and cryocoolers by a separate self-contained cryotherapy system.
Cryotherapy probes are used to treat a variety of diseases. The cryotherapy probes quickly freeze diseased body tissue, causing the tissue to die, after which it will be absorbed by the body or expelled by the body or sloughed off. Cryotherapy has traditionally been used within the operative setting to freeze liver and prostate tumors. Intraoperative ultrasound provided sufficient guidance for probe placement and progression of the ice front in relation to tumor margins. Cryotherapy for multiple outpatient treatments has a long history, due in part to its relatively painless delivery and ability to treat pain syndromes. The transition to outpatient cancer treatments requires rapidly freezing probes along with a convenient cryotherapy system. Without a relatively small, self-contained, easy-to-use cryosystem employing lower priced probes (i.e., currently each Endocare probe costs ˜$400-1500), the patient benefits of cryotherapy (i.e., lower pain, clear imaging of ablation zone and minimal scarring) will not adequately challenge the current popularity enjoyed by heat-based systems. For example, radiofrequency (RF) ablation has become the most common ablation modality perhaps more for its convenient set-up for physicians and lower disposable costs for hospital administrators than any distinct benefit over cryotherapy.
Percutaneous cryotherapy (PC) for breast, liver, kidney, bone and lung tumors has recently been described by Littrup, et al., copies of which are attached as Appendices A and B of U.S. Prov. Pat. Appl. Nos. 60/440,541 and 60/440,662, both of which have been incorporated by reference. PC monitoring is more difficult with standard ultrasound since it visualizes the treatment site from limited external positions. Therefore, CT and MRI have become the PC guidance modalities of choice due to their circumferential imaging and multi-slice rendering of a three dimensional volume. The phase change that occurs when tissue freezes (and resultant necrotic treatment margins) is much better seen by US, CT or MRI than the ablation margins of heat-based therapies. In addition, the necrotic treatment margin is much smoother and more predictable for ice than heat. When compared to heat-based ablation techniques, PC treatments are relatively painless and better preserve the underlying collagenous architecture of the ablated tissue. This produces better healing and less tissue disruption during, or after, the procedure. As long as bowel and major nerves are avoided, PC cancer treatments can be performed with safety of adjacent tissues via accurate treatment planning.
Adequate coverage of the tumor by ice, but with minimal side-effects, often requires several accurately placed cryoprobes. Multiple patents and applications have been published which attempt to address these issues. These cover cryoprobe design or freeze method [Cryomedical Sciences (U.S. Pat. Nos. 5,254,116 and 5,334,181); Endocare (U.S. Pat. Nos. 5,800,487 and 5,800,488); Cryogen (U.S. Pat. Nos. 5,910,104 and 6,475,212); Galil (U.S. Pat. Nos. 6,142,991 and 6,179,831)], computer controlled/interaction [Endocare (U.S. Pat. No. 6,139,544 and U.S. Pat. Publ. No. 2002/0016540A1); Cryogen (U.S. Pat. Nos. 5,513,742 and 6,471,694)] or MRI guidance [Galil (U.S. Pat. No. 5,978,697)]. Each of the foregoing patents and publications is incorporated herein by reference for all purposes. The Cryomedical Sciences efforts attempted to combat the flow difficulties encountered by liquid nitrogen (LN2) in smaller probes (e.g., ≦3 mm) but required a highly complex system using large LN2 volumes. While the Cryogen patents referred to a closed-loop gas system, no thermodynamic optimization was described to reduce engineering complexity. Therefore, companies with units which use large flow rates, or amounts of gas, to produce maximal freeze capacity per probe generally acknowledge the desire for an open system since the required compressors for such closed systems would become too large, expensive and unwieldy for portable use. In addition, the lack of optimized cryogenic design and probe configuration to produce the greatest freeze power for the minimal gas flow configuration prevents the design of smaller (i.e., <1.5 mm) probe diameters. While Galil has a 1.5 mm probe, its freeze capacity remains less than the Endocare 2.4 mm probe.
A combined effort is needed to optimize cryoprobes and the main driving system. A variety of cryotherapy instruments, variously referred to as cryoprobes, cryotherapy ablation devices, cryostats and cryocoolers, have become available. Currently preferred cryotherapy systems use Joule-Thomson (JT) cooling in devices known as JT cryostats. These devices take advantage of the fact that non-ideal gases, when rapidly expanded, become extremely cold. In these devices, a high pressure gas such as argon or nitrogen is expanded through a nozzle inside a small cylindrical sheath made of steel, and the JT expansion cools the steel sheath to sub-freezing cryogenic temperature very rapidly. An exemplary device is illustrated in U.S. Pat. No. 3,800,552, the entire disclosure of which is herein incorporated by reference for all purposes. This patent shows a basic Joule-Thomson probe with a sheath made of metal, a fin-tube helical gas supply line leading into a Joule-Thomson nozzle which directs expanding gas into the probe. Expanded gas is exhausted over the fin-tube helical gas supply line, and pre-cools incoming high pressure gas in what is known as a ‘counterflow heat exchanger’. The counterflow heat exchanger is beneficial because by pre-cooling incoming gas with the outgoing gas flow the probe obtains lower temperatures.
U.S. Pat. No. 5,522,870, the entire disclosure of which is herein incorporated by reference for all purposes, applies the general concepts of Joule-Thomson devices to a device which is used first to freeze tissue and then to thaw the tissue with a heating cycle. Nitrogen is supplied to a Joule-Thomson nozzle for the cooling cycle, and helium is supplied to the same Joule-Thomson nozzle for the warming cycle. Preheating of the helium is used to provide warming to a sufficiently high temperature. Furthermore, since the helium gas inversion temperature of approximately −240° C. is well below the base temperature of liquid nitrogen (−193° C.) helium is essentially an ideal gas at −240° C. and higher temperatures, and hence it does not cool during the gas expansion process. Various cryocoolers use mass flow warming, flushed backwards through the probe, to warm the probe after a cooling cycle [Lamb, Refrigerated Surgical Probe, U.S. Pat. No. 3,913,581; Longsworth, Cryoprobe, U.S. Pat. No. 5,452,582]. Each of these patents is also incorporated herein by reference for all purposes. A deficiency to broad adoption of gas-based systems by physicians and hospitals appears to be their lack of efficient self-contained systems.
Finally, cryotherapy needs to be considered as an adjuvant, or complementary, treatment with other cancer therapies. Successful reports from many papers on image-guided tumor ablation (including both heat-based and cryotherapy) were noted at the Radiological Society of North America's annual meeting for 2002 and 2003. Several prominent radiologists considered it to be “the fourth branch of oncology”, in conjunction with surgery, radiation therapy and chemotherapy. Littrup, et al, have also noted the possible potentiation of cryotherapy, as well as reduced bleeding risk, by pre-injecting the region to be frozen with macro-aggregated albumin (MAA), hypertonic saline and epinephrine. This technique has been described by Dr. Order for treatment of pancreatic cancer with p32, whereby the MAA creates an interstitial ‘gel’ effect and thus decreases subsequent fluid extravasation of the p32 out of the tumor injection site (U.S. Pat. Nos. 5,538,726 and 5,424,288). In addition, injection of radiotherapeutic, or chemotherapeutic, agents directly into the tumor before or after the freeze may provide more thorough tumor ablation. Combining cryotherapy with radiation therapy, or chemotherapy, may reduce the overall risks of either chemotherapy or radiation therapy alone. Therefore, probe modifications which could deliver fluid through the probe, associated sheath system, or separate probe injection system would be of distinct benefit for future cryotherapy applications. In addition, probe modifications to allow minimal size with injection capacity would also benefit and re-invigorate the interest in PC for localized nerve ablation in pain management.